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Natural Experiment (natural + experiment)
Selected AbstractsUNITED STATES V. BOOKER AS A NATURAL EXPERIMENT: USING EMPIRICAL RESEARCH TO INFORM THE FEDERAL SENTENCING POLICY DEBATE,CRIMINOLOGY AND PUBLIC POLICY, Issue 3 2007PAUL J. HOFER Research Summary: In United States v. Booker, the U.S. Supreme Court held that the federal sentencing guidelines must be considered advisory, rather than mandatory, if they are to remain constitutional under the Sixth Amendment. Since the decision, the U.S. Sentencing Commission has provided policy makers with accurate and current data on changes and continuity in federal sentencing practices. Unlike previous changes in legal doctrine, Booker immediately increased the rates of upward and downward departures from the guideline range. Government-sponsored downward departures remain the leading category of outside,the-range sentences. The rate of within-range sentences, although lower than in the period immediately preceding Booker, remains near rates observed earlier in the guidelines era. Despite the increase in departures, average sentence lengths for the overall caseload remain stable, because of offsetting increases in the seriousness of the crimes being sentenced and in the severity of penalties for those crimes. Analyses of the reasons that judges reported for downward departures suggest that treatment of criminal history and offender characteristics are the two leading areas of dissatisfaction with the guidelines. Policy Implications: Assessment of changes in sentencing practices following Booker by different observers depends partly on competing institutional perspectives and on different degrees of trust in the judgment of judges, prosecutors, the Sentencing Commission, and Congress. No agreement on whether Booker has bettered or worsened the system can be achieved until agreement exists on priorities among the purposes of sentencing and the goals of sentencing reform. Both this lack of agreement and an absence of needed data make consensus on Booker's effects on important sentencing goals, such as reduction of unwarranted disparity, unlikely in the near future. Similarly, lack of baseline data before Booker on the effectiveness of federal sentencing at crime control makes before-after comparisons impossible. Despite these limitations, research provides a sounder framework for policy making than do anecdotes or speculation and sets valuable empirical parameters for the federal sentencing policy debate. [source] INDEPENDENCE DAY FOR THE ,OLD LADY': A NATURAL EXPERIMENT ON THE IMPLICATIONS OF CENTRAL BANK INDEPENDENCE,THE MANCHESTER SCHOOL, Issue 3 2007JAGJIT S. CHADHA Central bank independence is widely thought be a sine qua non of a credible commitment to price stability. The surprise decision by the UK government to grant operational independence to the Bank of England in 1997 affords us a natural experiment with which to gauge the impact on the yield curve from the adoption of central bank independence. We document the extent to which the decision to grant independence was ,news' and illustrate that the reduction in medium- and long-term nominal interest rates was some 50 basis points, which we show to be consistent with a sharp increase in policy-maker's aversion to inflation deviations from target. We therefore suggest that central bank independence represents one of the clearest signals available to elected politicians about their preferences on the control of inflation. [source] Enhancing Security Value by Ownership Restrictions: Evidence from a Natural ExperimentFINANCIAL MANAGEMENT, Issue 4 2005Amar Gande We present new evidence from a natural experiment to show circumstances in which ownership restrictions can enhance value. Our evidence is based on multiple restricted bond issues by an emerging market issuer at 150 basis points lower than comparable bonds, resulting in a billion dollars saving. This is intriguing: how can an emerging market issuer with junk bond ratings obtain such low yields? We argue ownership restrictions enhance value since they enable an issuer to precommit to renegotiate efficiently with a favored clientele in the potential default states, thereby circumventing deadweight costs of prolonged negotiations, particularly when the restricted clientele also values the underlying collateral higher than other investors. Ownership restrictions can also result in a transfer of value from holders of unrestricted bonds to holders of restricted bonds because of implicit seniority of the latter. We empirically test and find support for both value enhancement and value transfer and show robustness to several alternative explanations. Our evidence suggests that firms can benefit from designing securities with ownership restrictions, by offering new securities exclusively to investors who value them the most. [source] Evaluation of Nationally Mandated Drug Use Reviews to Improve Patient Safety in Nursing Homes: A Natural ExperimentJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 6 2005Becky Briesacher PhD Objectives: To test whether nationally required drug use reviews reduce exposure to inappropriate medications in nursing homes. Design: Quasi-experimental, longitudinal study. Setting: Data source is the 1997,2000 Medicare Current Beneficiary Survey, a nationally representative survey of Medicare beneficiaries. Participants: Nationally representative population sample of 8 million nursing home (NH) residents (unweighted n=2,242) and a comparative group of 2 million assisted living facility (ALF) residents (unweighted n=664). Measurements: Prevalence and incident use of 38 potentially inappropriate medications compared before and after the policy: 32 restricted for all NH residents and six for residents with certain conditions. Inappropriate medications were stratified by potential for legitimate exceptions: always avoid, rarely appropriate, or some acceptable indications. Results: In July 1999, the Centers for Medicare and Medicaid Services (CMS) mandated expansions to the drug use review policy for nursing home certification. Using explicit criteria, surveyors and consultant pharmacists must evaluate resident records for potentially inappropriate medication exposures and related adverse drug reactions. Nursing homes in noncompliance may receive citations for deficient care. Before the CMS policy, 28.8% (95% confidence interval (CI)=27.3,30.3) of Medicare beneficiaries in NHs and 22.4% (95% CI=19.8,25.0) in ALFs received potentially inappropriate medications. Nearly all prepolicy use came from medications with some acceptable indications: 23.4% in NHs (95% CI=20.4,26.4) and 18.0% in ALFs (95% CI=15.6,20.4). After the policy, exposures in NHs declined to 25.6% (95% CI=24.1,27.1, P<.05), but similar declines occurred in ALFs (19.0%, 95% CI=16.7,21.3, nonsignificant). Postpolicy use of inappropriate medications with exempted indications remained high, and more than half was incident use: 20.6% of NH residents (95% CI=19.0,22.0) and 15.6% of ALF residents (95% CI=15.2,15.7). Use of drugs that are restricted with certain diseases increased 33% in NHs between 1997 and 2000 (from 9.3% to 13.2%; P<.05). Multivariate results detected no postpolicy differences in inappropriate drug use between long-term care facilities with mandatory drug use reviews and those without. Conclusion: Some postpolicy declines were noted in NH use of potentially inappropriate medications, but the decrease was uneven and could not be attributed to the national drug use reviews. This study is the first evaluation of the CMS policy, and it highlights the unclear effectiveness of drug use reviews to improve patient safety in NHs even though state and federal agencies have widely adopted this strategy. [source] The Causal Effect of Election Delay on Union Win Rates: Instrumental Variable Estimates from Two Natural ExperimentsINDUSTRIAL RELATIONS, Issue 3 2010CHRIS RIDDELL The role of election delay in union organizing campaigns has become a key policy issue in several countries. Previous studies have documented a negative correlation between delay and union success. However, elections are generally not randomly delayed; in particular, election delay is correlated with various "hard-to-observe" union and employer strategies. This article exploits several exogenous sources of variation in election delay to estimate a causal model. The results indicate that two-stage least squares estimates of the causal effect of election delay on union success are twice the magnitude of standard OLS estimates. [source] Novel ecosystems resulting from landscape transformation create dilemmas for modern conservation practiceCONSERVATION LETTERS, Issue 3 2008David B. Lindenmayer Abstract Introduction: Novel ecosystems occur when new combinations of species appear within a particular biome due to human activity, environmental change, or impacts of introduced species. Background: Managing the trajectory of ecosystems toward desired outcomes requires an understanding of the means by which they developed. To facilitate this understanding, we present evidence for the development of a novel ecosystem from a natural experiment focusing on 52 woodland remnants surrounded by maturing stands of exotic radiata pine. Results: Bird community composition changed through time resulting in a unique blend of tall closed forest and open-woodland birds that previously did not occur in the study area, nor in the region's tall closed forest or open-woodland biomes. Conclusion: Novel ecosystems will become increasingly common due to climate change, raising complex management and ethical dilemmas for policy makers and resource managers. [source] Tracking diabetes in Albania: a natural experiment on the impact of modernization on healthDIABETIC MEDICINE, Issue 2 2002L Shapo No abstract is available for this article. [source] EMPLOYMENT EFFECTS OF TWO NORTHWEST MINIMUM WAGE INITIATIVESECONOMIC INQUIRY, Issue 1 2007LARRY D. SINGELL Jr This article exploits a natural experiment initiated by Oregon and Washington voter referendums to show that the minimum wage is a blunt instrument that differentially affects low-wage workers within and across industries. Specifically, employment growth specifications indicate that the minimum wage generates consistently negative employment effects for eating and drinking workers where the minimum is shown to be relatively binding, but not for hotel and lodging workers where the minimum is less binding. Regressions using job-specific want-ad data from Portland and Seattle newspapers also indicate a reduction in hiring solicitation relating to the extent that the minimum wage binds. (JEL J31, J38) [source] From Great Depression to Great Credit Crisis: similarities, differences and lessonsECONOMIC POLICY, Issue 62 2010Miguel Almunia Summary The Great Depression of the 1930s and the Great Credit Crisis of the 2000s had similar causes but elicited strikingly different policy responses. While it remains too early to assess the effectiveness of current policy, it is possible to analyse monetary and fiscal responses in the 1930s as a natural experiment or counterfactual capable of shedding light on the impact of current policies. We employ vector autoregressions, instrumental variables, and qualitative evidence for 27 countries in the period 1925,39. The results suggest that monetary and fiscal stimulus was effective -- that where it did not make a difference it was not tried. They shed light on the debate over fiscal multipliers in episodes of financial crisis. They are consistent with multipliers at the higher end of those estimated in the recent literature, and with the argument that the impact of fiscal stimulus will be greater when banking systems are dysfunctional and monetary policy is constrained by the zero bound. --- Miguel Almunia, Agustín Bénétrix, Barry Eichengreen, Kevin H. O'Rourke and Gisela Rua [source] A Shred of Credible Evidence on the Long-run Elasticity of Labour SupplyECONOMICA, Issue 308 2010ORLEY ASHENFELTER All public policies regarding taxation and the redistribution of income rely on assumptions about the long-run effect of wages rates on labour supply. The variation in existing estimates calls for a simple, natural experiment in which men can change their hours of work, and in which wages have been exogenously and permanently changed. We use a panel dataset of taxi drivers who choose their own hours, and who experienced two exogenous permanent fare increases, and estimate an elasticity of labour supply of ,0.2, implying that income effects dominate substitution effects in the long-run labour supply of males. [source] Intertemporal Substitution of Effort: Some Empirical EvidenceECONOMICA, Issue 280 2003John G. Treble The labour economics literature refers often to effort, but there is little empirical evidence as to how productivity and effort respond to wage rate variations. An unusual natural experiment in which wage rates suffered an exogenous change of two weeks' duration gives some insight into the magnitude of this effect. For a group of workers in Victorian County Durham, the effort response, measured as the impact of a temporary wage rate change on output per shift, dominates the response of attendance. Comparison of the estimates presented here with those in Treble (Journal of Economic History, 61, 414,38, 2001) suggests that the effects are short lived. [source] Enhancing Security Value by Ownership Restrictions: Evidence from a Natural ExperimentFINANCIAL MANAGEMENT, Issue 4 2005Amar Gande We present new evidence from a natural experiment to show circumstances in which ownership restrictions can enhance value. Our evidence is based on multiple restricted bond issues by an emerging market issuer at 150 basis points lower than comparable bonds, resulting in a billion dollars saving. This is intriguing: how can an emerging market issuer with junk bond ratings obtain such low yields? We argue ownership restrictions enhance value since they enable an issuer to precommit to renegotiate efficiently with a favored clientele in the potential default states, thereby circumventing deadweight costs of prolonged negotiations, particularly when the restricted clientele also values the underlying collateral higher than other investors. Ownership restrictions can also result in a transfer of value from holders of unrestricted bonds to holders of restricted bonds because of implicit seniority of the latter. We empirically test and find support for both value enhancement and value transfer and show robustness to several alternative explanations. Our evidence suggests that firms can benefit from designing securities with ownership restrictions, by offering new securities exclusively to investors who value them the most. [source] Non-random patterns in the Yellowstone ecosystem: inferences from mammalian body size, order and biogeographical affinityGLOBAL ECOLOGY, Issue 2 2007Judsen E. Bruzgul ABSTRACT Aim, Our aim was to investigate how the environment, species characteristics and historical factors at the subcontinental scale affect patterns of diversity. We used the assembly of the Yellowstone biota over the past 10,000 years as a natural experiment for investigating the processes that generate a modern non-volant mammal species pool. Location, The data represent species from throughout North America with special attention to the non-volant mammals of Yellowstone National Park, USA. Methods, We used digitized range maps to determine biogeographical affinity for all non-volant mammals in the Rocky Mountains, Deserts and Great Plains biogeographical regions of North America. This biogeographical affinity, along with taxonomic order and body size class, was used to test whether non-random patterns exist in the assemblage of Yellowstone non-volant mammals. These characteristics were also used to investigate the strength of non-random processes, such as habitat or taxon filtering, on particular groups of species or individual species. Results, Our results indicated that the Yellowstone fauna is composed of a non-random subset of mammals from specific body size classes and with particular biogeographical affinities. Analyses by taxonomic order found significantly more Carnivora from the Rocky Mountains region and significantly fewer Rodentia from the Deserts region than expected from random assembly. Analyses using body size classes revealed deviations from expectations, including several significant differences between the frequency distribution of regional body sizes and the distribution of those species found within Yellowstone. Main conclusions, Our novel approach explores processes affecting species pool assembly in the Yellowstone region and elsewhere, and particularly identifies unique properties of species that may contribute to non-random assembly. Focusing on the mechanisms generating diversity, not just current diversity patterns, will assist the design of conservation strategies given future environmental change scenarios. [source] Assessing the Value of the NHIS for Studying Changes in State Coverage Policies: The Case of New YorkHEALTH SERVICES RESEARCH, Issue 6p2 2007Sharon K. Long Research Objective. (1) To assess the effects of New York's Health Care Reform Act of 2000 on the insurance coverage of eligible adults and (2) to explore the feasibility of using the National Health Interview Survey (NHIS) as opposed to the Current Population Survey (CPS) to conduct evaluations of state health reform initiatives. Study Design. We take advantage of the natural experiment that occurred in New York to compare health insurance coverage for adults before and after the state implemented its coverage initiative using a difference-in-differences framework. We estimate the effects of New York's initiative on insurance coverage using the NHIS, comparing the results to estimates based on the CPS, the most widely used data source for studies of state coverage policy changes. Although the sample sizes are smaller in the NHIS, the NHIS addresses a key limitation of the CPS for such evaluations by providing a better measure of health insurance status. Given the complexity of the timing of the expansion efforts in New York (which encompassed the September 11, 2001 terrorist attacks), we allow for difference in the effects of the state's policy changes over time. In particular, we allow for differences between the period of Disaster Relief Medicaid (DRM), which was a temporary program implemented immediately after September 11th, and the original components of the state's reform efforts,Family Health Plus (FHP), an expansion of direct Medicaid coverage, and Healthy New York (HNY), an effort to make private coverage more affordable. Data Sources. 2000,2004 CPS; 1999,2004 NHIS. Principal Findings. We find evidence of a significant reduction in uninsurance for parents in New York, particularly in the period following DRM. For childless adults, for whom the coverage expansion was more circumscribed, the program effects are less promising, as we find no evidence of a significant decline in uninsurance. Conclusions. The success of New York at reducing uninsurance for parents through expansions of both public and private coverage offers hope for new strategies to expand coverage. The NHIS is a strong data source for evaluations of many state health reform initiatives, providing a better measure of insurance status and supporting a more comprehensive study of state innovations than is possible with the CPS. [source] Closing call auctions and liquidityACCOUNTING & FINANCE, Issue 4 2005Michael Aitken G14; G15 Abstract The present paper examines the impact of closing call auctions on liquidity. It exploits the natural experiment offered by the introduction of a closing call auction on the Australian Stock Exchange on 10 February 1997. The introduction of the closing call auction is associated with a reduction in trading volume at the close of continuous trading. However, bid-ask spreads during continuous trading are largely unaffected by the introduction of the closing call auction. Therefore, closing call auctions consolidate liquidity at a single point in time without having any adverse effect on the cost of trading. [source] Factors affecting the survival of founding individuals in translocated New Zealand Saddlebacks Philesturnus carunculatusIBIS, Issue 4 2007SABRINA S. TAYLOR Successful founders of new populations may represent a non-random sample of potential founding individuals. Using a recent Saddleback Philesturnus carunculatus translocation as a natural experiment, we related morphology, parasite load and genetic variation of translocated individuals to subsequent survivorship to assess the traits of successful founders. We also included capture location and holding time in our models to account for variables particular to translocations. Generalized linear model results suggest that, in addition to capture location, poor body condition (males) and the presence of ectoparasites (females) significantly reduced survivorship. Despite recent claims in the literature, we found no evidence that genetic variation was associated with survivorship or parasite load. [source] The Regulation of Public Company Auditing: Evidence from the Transition to AS5JOURNAL OF ACCOUNTING RESEARCH, Issue 4 2010RAJIB DOOGAR ABSTRACT The replacement of Auditing Standard No. 2 (AS2) by Auditing Standard No. 5 (AS5) creates a natural experiment that sheds light on (1) potential inefficiencies caused by regulatory responses to a political crisis and (2) audit efficiency and effectiveness improvements resulting from the risk-based approach embodied in AS5. We study these effects by examining the impact of AS5 on audit fees. We find that AS5 audit fees are aligned with auditee fraud risk, but not AS2 audit fees. Second, relative to AS2 benchmark levels, AS5 audit fees are, on average, lower for all auditees. Third, relative to AS2 benchmarks, AS5 fees are lower for lower-fraud-risk auditees but greater for higher-fraud-risk auditees. Overall, the evidence is consistent with (1) initial overregulation (via AS2) followed by reform (via AS5) and (2) auditors deploying a risk-based audit approach to obtain both efficiency and potential effectiveness gains in audit production. [source] Urbanization and the more-individuals hypothesisJOURNAL OF ANIMAL ECOLOGY, Issue 2 2010Claudia Chiari Summary 1.,Urbanization is a landscape process affecting biodiversity world-wide. Despite many urban,rural studies of bird assemblages, it is still unclear whether more species-rich communities have more individuals, regardless of the level of urbanization. The more-individuals hypothesis assumes that species-rich communities have larger populations, thus reducing the chance of local extinctions. 2.,Using newly collated avian distribution data for 1 km2 grid cells across Florence, Italy, we show a significantly positive relationship between species richness and assemblage abundance for the whole urban area. This richness,abundance relationship persists for the 1 km2 grid cells with less than 50% of urbanized territory, as well as for the remaining grid cells, with no significant difference in the slope of the relationship. These results support the more-individuals hypothesis as an explanation of patterns in species richness, also in human modified and fragmented habitats. 3.,However, the intercept of the species richness,abundance relationship is significantly lower for highly urbanized grid cells. Our study confirms that urban communities have lower species richness but counters the common notion that assemblages in densely urbanized ecosystems have more individuals. In Florence, highly inhabited areas show fewer species and lower assemblage abundance. 4.,Urbanized ecosystems are an ongoing large-scale natural experiment which can be used to test ecological theories empirically. [source] Spatial synchrony in field vole Microtus agrestis abundance in a coniferous forest in northern England: the role of vole-eating raptorsJOURNAL OF APPLIED ECOLOGY, Issue 2000S.J. Petty 1.,The regional synchrony hypothesis (RSH) states that synchrony in microtine abundance over large geographical areas is caused by nomadic avian predators that specialize on small mammals for food. This has proved a difficult hypothesis to test because experiments at an appropriate scale are almost impossible. 2.,We used the decline of the most abundant, nomadic vole-eating raptors in an extensive conifer forest in northern England (Kielder Forest) as a natural experiment to evaluate their influence on synchronizing voles at different spatial scales. Field vole populations fluctuated on a 3,4-year cycle of abundance, similar to the periodicity in central Fennoscandia. 3.,Over a 23-year period, the combined numbers and density of kestrels and short-eared owls significantly declined. If these raptors were responsible for synchronizing vole abundance, the decline should have been associated with a decrease in synchrony. We could find no change in synchrony during the period of the greatest decline in kestrel and short-eared owl numbers (1980,97). 4.,In Kielder, vole abundance has been shown to change in a wave-like manner, with synchrony in the direction of the wave being 5,10-fold smaller than that reported in Fennoscandia. Tawny owls are sedentary and the most abundant vole-eating raptor in our study area, and might have an equalizing influence on vole abundance over smaller areas if they foraged in a density-dependent manner and responded functionally to increasing vole density. If this was the case, spatial variability in vole density should have been less in occupied than unoccupied owl territories, especially in years of low vole density when owls could take a larger proportion of the standing crop of voles. Even though tawny owls caught a significant proportion of the vole population, we could find no difference in variation in vole density between owl territories that were unoccupied, occupied with no breeding attempt, or occupied with a successful breeding attempt. 5.,We conclude that the small-scale synchrony in field vole abundance is unlikely to be caused by avian predators. Instead, it is more likely to be related to the pattern of clear-cutting that has developed in Kielder, which restricts vole dispersal. If this assumption is correct, we would predict more widespread synchrony in vole abundance in first-generation forests when extensive areas are planted over short periods of time, and this is supported by anecdotal evidence. These conclusions indicate that foresters may be able to manipulate the spatial dynamics of voles and vole predators by varying patch sizes within forests. [source] Tax Clientele Effects in the Term Structure of UK Interest RatesJOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 3-4 2001Eric J. Levin This paper tests for tax clientele effects in the term structure of UK interest rates. Five empirical models of the term structure of interest rates, incorporating tax effects, are estimated with daily data covering the period 31 March, 1995 to 3 August, 1995. In May 1995, the British government announced its intention to eliminate the tax exemption on capital gains from government bonds, but subsequently in July 1995 backtracked on some of its initial proposals. This period therefore forms the basis of a crude natural experiment in the sense that it provides an opportunity to examine tax clientele effects ,before' and ,after' an event which should have levelled greatly the taxing of government bonds. The empirical analysis suggests large tax clientele effects. However, there is little evidence of tax-specific term structures of interest rates. [source] Seed predation during general flowering events of varying magnitude in a Malaysian rain forestJOURNAL OF ECOLOGY, Issue 4 2007I-FANG SUN Summary 1The lowland dipterocarp forests of Southeast Asia exhibit interspecifically synchronized general flowering (GF) and mast fruiting at irregular multi-year intervals of 1 to 11 years. The predator satiation hypothesis (PSH) posits that GF events enhance seed survival by reducing the survival, reproduction and population sizes of seed predators between GF events, and then satiating the reduced seed predator populations during GF events. 2Three GF events of different magnitudes occurred in Pasoh Forest Reserve, Peninsular Malaysia, during 2001, 2002 and 2005. We exploited this natural experiment to test two predictions of the PSH. The first prediction was that seed survival should increase with the magnitude of the GF event. The second prediction was that seed predation should decrease with time since the previous GF event. 3A reproductive survey of all (c. 900) dipterocarp trees 30 cm d.b.h. in a 50 ha plot showed that flowering pervasiveness (the proportion of dipterocarp species participating) was high and similar in all three GF events. However, relative flowering magnitudes (measured by an index of individual tree participation and flowering intensity in Shorea species) were 2, 5 and 8 for the 2001, 2002 and 2005 GF events, respectively. 4The percentage of Shorea seeds surviving pre- and post-dispersal predation increased with the magnitude of GF events, which is consistent with the first prediction. 5Pre-dispersal insect seed predators consumed 12.9%, 11.2% and 3.4% of Shorea seeds in the 2001, 2002 and 2005 GF events, respectively, which is consistent with both predictions. 6Pre-dispersal seed predation by primates (mainly leaf monkeys) increased from 11.9% to 38.6% then fell to 9.3% in the 2001, 2002 and 2005 GF events, respectively. 7Predator satiation occurred only at population and community levels. At the individual tree level there was no relationship between the percentage of seeds surviving pre- and post-dispersal seed predation and variation in seed crop size or seed density beneath the tree. This suggests that attempts to test the PSH on the scale of individual trees may miss key community level effects. 8Our results suggest a more significant role of pre-dispersal seed predation in the evolution of reproductive synchrony than was recognized in the original statement of the PSH. [source] HMO Participation in Medicare+ChoiceJOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 3 2005John Cawley In recent years, many health maintenance organizations (HMOs) have exited Medicare+Choice (M+C), the program that provides a managed-care option to Medicare. This paper answers the following questions: How does the equilibrium number of HMOs participating in county M+C markets vary with the capitation payment they are offered? How large a payment is required at the margin to ensure that various percentages of county markets have a M+C HMO, or to ensure that various percentages of Medicare beneficiaries have the choice of a M+C plan in their county of residence? The strategy for identifying the effect of government payment on HMO participation relies on a natural experiment; in 1997, Congress divorced M+C payments to HMOs from changes in underlying costs. The results in this paper suggest that the Centers for Medicare & Medicaid Services (CMS) has consistently underestimated the payment necessary to support HMOs in rural, sparsely populated areas. We also find that it would require a large incremental payment to support HMOs in M+C for the final 10% of counties or final 10% of Medicare beneficiaries. [source] Effect of floating nest platforms on the breeding performance of Black TernsJOURNAL OF FIELD ORNITHOLOGY, Issue 2 2006David A. Shealer ABSTRACT In 2003 and 2004, we placed 41 floating nest platforms on Grassy Lake in southeastern Wisconsin (USA) to test the hypothesis that reproductive success of Black Terns (Chlidonias niger) is limited by the quality of suitable nesting habitat. Extreme differences in water levels between these 2 yr provided a natural experiment to evaluate the effectiveness of the nest platforms during a drought year (2003) when natural nesting substrate was abundant, and a flood year (2004) when natural substrate was limited during the peak nesting period. Terns nested on 27 of 41 (66%) of the platforms in 2003 and 26 of 41 (63%) in 2004. No difference in the occupancy rate of platforms and natural nests was evident in 2003, but the pattern of clutch initiations early in the season in 2004 indicated that platforms were preferred over natural substrates. In 2003, nest survival rates did not differ between nests placed on platforms and those placed on natural substrates, but platform nests had significantly higher hatching success and nest survival rates in 2004. Both the Kaplan-Meier and Apparent Nest Success methods of calculating nest survival provided similar estimates. In both years, eggs laid on platforms were significantly larger than those laid on natural substrates, suggesting that platforms were occupied by high-quality birds. Our study indicates that floating nest platforms can be an effective management tool to enhance nesting habitat for Black Terns and other aquatic birds that construct floating nests, primarily because platforms provide nest sites when natural sites are not available due to flooding. Nest platforms also may be useful for addressing questions concerning habitat selection and parental quality. SINOPSIS De 2003-2004 colocamos 41 plataformas flotantes para poner aprueba la hipótesis que el éxito reproductivo de la gaviota Chlidonias níger, esta limitado por la calidad y lo apropiado del hábitat de anidamiento. El estudio se llevó a cabo en el Grassy Lake, Wisconsin. Extremos (bajos y altos) en los niveles de agua, causados por sequía (2203) y fuertes lluvias (2004) proveyeron el escenario adecuado para evaluar la efectividad de las plataformas. Las gaviotas anidaron en 27 (66%) de las 41 plataformas en el 2003 y en 26 (63%) de las 41 en el 2004. No se encontraron diferencias en la tasa de uso de las plataformas y áreas naturales en el 2003, pero el inicio de las camadas temprano en la temporada durante el 2004, dieron a indicar que las plataformas fueron preferidas a los lugares naturales. Durante el 2003, no hubo diferencia en la tasa de supervivencia de nidos en plataformas y o en áreas naturales. Sin embargo, durante el 2004 el éxito de eclosionamiento, de los nidos y la supervivencia fue mas alto en las plataformas. Tanto el método Kaplan-Meier como el "Aparente Éxito de Anidamiento", utilizados para calcular la supervivencia de los nidos, ofrecieron resultados similares. En ambos años el tamaño de los huevos fue mayor en las plataformas que en áreas naturales, lo que implica que las primeras fueron utilizadas por aves sumamente vigorosas o de alta calidad. El estudio indica que las plataformas flotantes pueden ser una herramienta de manejo adecuada para mejorar el hábitat de anidamiento de la gaviota estudiada, al igual que otras aves que construyen nidos flotantes. Las plataformas proveen de lugares de anidamientos cuando no hay disponible lugares naturales debido a inundaciones. Las plataformas de anidamiento muy bien pudieran proveer de información útil con respecto a la selección de hábitat y la calidad del cuidado parental. [source] Do financial incentives help low-performing schools attract and keep academically talented teachers?JOURNAL OF POLICY ANALYSIS AND MANAGEMENT, Issue 3 2010Evidence from California This study capitalizes on a natural experiment that occurred in California between 2000 and 2002. In those years, the state offered a competitively allocated $20,000 incentive called the Governor's Teaching Fellowship (GTF) aimed at attracting academically talented, novice teachers to low-performing schools and retaining them in those schools for at least four years. Taking advantage of data on the career histories of 27,106 individuals who pursued California teaching licenses between 1998 and 2003, we use an instrumental variable strategy to estimate the unbiased impact of the GTF on the decisions of recipients to begin working in low-performing schools within 2 years after licensure program enrollment. We estimate that GTF recipients would have been less likely to teach in low-performing schools than observably similar counterparts had the GTF not existed, but that acquiring a GTF increased their probability of doing so by 28 percentage points. Examining retention patterns, we find that 75 percent of both GTF recipients and nonrecipients who began working in low-performing schools remained in such schools for at least four years. © 2010 by the Association for Public Policy Analysis and Management. [source] Public transit and the spatial distribution of minority employment: Evidence from a natural experimentJOURNAL OF POLICY ANALYSIS AND MANAGEMENT, Issue 3 2003Harry J. Holzer A recent expansion of the San Francisco Bay Area's heavy rail system represents an exogenous change in the accessibility of inner-city minority communities to a concentrated suburban employment center. We evaluate this natural experiment by conducting a two-wave longitudinal survey of firms, with the first wave of interviews conducted immediately before the opening of service, and the second wave approximately a year later. Within-firm changes in the propensity to hire minority workers for firms near the station were compared with those located farther away. Also estimated was the effect of employer distance to the new stations on changes in propensity to hire minorities. Results indicate a sizable increase in the hiring of Latinos near the new stations, but little evidence of an effect on black hiring rates. © 2003 by the Association for Public Policy Analysis and Management. [source] TIEBOUT DYNAMICS: NEIGHBORHOOD RESPONSE TO A CENTRAL-CITY/SUBURBAN HOUSE-PRICE DIFFERENTIAL,JOURNAL OF REGIONAL SCIENCE, Issue 4 2007Paul Thorsnes ABSTRACT We take advantage of an unusual natural experiment,a high-quality 1920s subdivision split neatly in half by a central-city/suburban boundary,to study the response over 30 years to the relative decline in the quality of central-city services since the 1960s. As expected, a large sale price differential opens in the 1960s. Demographic characteristics are nevertheless similar across the boundary. Survey data indicate Tiebout sorting: the central city side attracts households who prefer alternatives to suburban public schools. Children attend parochial and public "magnet" schools. A neighborhood association supplements municipal services. Rigid service district boundaries inhibit closure of the house-price differential. [source] Physicians' Labour Supply: The Wage Impact on Hours and Practice CombinationsLABOUR, Issue 4 2005Erik Magnus Sæther Increased wages is one instrument for boosting the hours provided by the personnel to the prioritized sub-markets. This study applies an econometric framework that allows for non-convex budget sets, non-linear labour supply curves and imperfect markets with institutional constraints. The labour supply decision is viewed as a choice from a set of discrete alternatives (job packages) in a structural labour supply model estimated on Norwegian micro data. An out-of-sample prediction is also presented and evaluated by means of a natural experiment. [source] Host specificity and reproductive success of yucca moths (Tegeticula spp.MOLECULAR ECOLOGY, Issue 24 2009Lepidoptera: Prodoxidae) mirror patterns of gene flow between host plant varieties of the Joshua tree (Yucca brevifolia: Agavaceae) Abstract Coevolution between flowering plants and their pollinators is thought to have generated much of the diversity of life on Earth, but the population processes that may have produced these macroevolutionary patterns remain unclear. Mathematical models of coevolution in obligate pollination mutualisms suggest that phenotype matching between plants and their pollinators can generate reproductive isolation. Here, we test this hypothesis using a natural experiment that examines the role of natural selection on phenotype matching between yuccas and yucca moths (Tegeticula spp.) in mediating reproductive isolation between two varieties of Joshua tree (Yucca brevifolia var. brevifolia and Y. brevifolia var. jaegeriana). Using passive monitoring techniques, DNA barcoding, microsatellite DNA genotyping, and sibship reconstruction, we track host specificity and the fitness consequences of host choice in a zone of sympatry. We show that the two moth species differ in their degree of host specificity and that oviposition on a foreign host plant results in the production of fewer offspring. This difference in host specificity between the two moth species mirrors patterns of chloroplast introgression from west to east between host varieties, suggesting that natural selection acting on pollinator phenotypes mediates gene flow and reproductive isolation between Joshua-tree varieties. [source] Genetic diversity and population size: island populations of the common shrew, Sorex araneusMOLECULAR ECOLOGY, Issue 10 2007THOMAS A. WHITE Abstract Populations of many species are currently being fragmented and reduced by human interactions. These processes will tend to reduce genetic diversity within populations and reduce individual heterozygosities because of genetic drift, inbreeding and reduced migration. Conservation biologists need to know the effect of population size on genetic diversity, as this is likely to influence a population's ability to persist. Island populations represent an ideal natural experiment with which to study this problem. In a study of common shrews (Sorex araneus) on offshore Scottish islands, 497 individuals from 13 islands of different sizes and 6 regions on the mainland were trapped and genotyped at eight microsatellite loci. Previous genetic work had revealed that most of the islands in this study were highly genetically divergent from one another and the mainland. We found that most of the islands exhibited lower genetic diversity than the mainland populations. In the island populations, mean expected heterozygosity, mean observed heterozygosity and mean allelic richness were significantly positively correlated with log island size and log population size, which were estimated using habitat population density data and application of a Geographic Information System. [source] A socio-historical hypothesis for the diabetes epidemic in Chinese,Preliminary observations from Hong Kong as a natural experimentAMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 3 2009C.M. Schooling It has been hypothesized that the emerging epidemic of diabetes in economically transitioning or recently transitioned populations is due to mismatch between developmental and mature environments. We took advantage of migration within an ethnically homogenous population to investigate this hypothesis, and the potentially modifying role of postnatal growth conditions, proxied by greater height. We used multivariable logistic regression in a population-based cross-sectional study from 1994 to 1996 of 2,341 long-term Hong Kong residents aged 25,74 years, either born in contemporaneously developed Hong Kong or migrants from economically undeveloped Guangdong. Migrant status was not associated with clinically diagnosed diabetes, odds ratio 1.05 (95% confidence interval 0.69,1.58) in adult migrants compared to Hong Kong-born natives and 1.22 (0.83,1.80) in preadult migrants, adjusted for age, sex, socio-economic position, and lifestyle. However, the association of diabetes with migrant status varied with height, suggesting a potentially complex relationship between indicators of prenatal and postnatal nutritional exposures. Compared to tall Hong Kong-born natives, the odds ratio of diabetes was 2.36 (1.20,4.61) in tall migrants, 1.94 (1.07,3.53) in short Hong Kong-born natives, but 1.04 (0.48,2.23) in short adult migrants. Additionally adjusting for body mass index and waist-hip ratio had little effect, apart from attenuating the association between short height and diabetes prevalence in Hong Kong-born natives. Whether the current epidemic of diabetes is a long-standing effect of such mismatch or a "first-generation through effect" generated by rapid economic development causing disproportionate growth remains to be determined. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||||||||